EP1425767A1

EP1425767A1 - Micro-replicated miniaturised electric components

Info

Publication number: EP1425767A1
Application number: EP02724857A
Authority: EP
Inventors: Tapani Ryhänen; Hans Otto Scheck; Ove Asplunda ÖHMAN; Olle Larsson; Mike Read; Tomas LINDSTRÖM
Original assignee: Nokia Oyj; MIC AB; Nokia Inc
Current assignee: Nokia Oyj; MIC AB; Nokia Inc
Priority date: 2001-04-20
Filing date: 2002-04-22
Publication date: 2004-06-09
Also published as: US20040195000A1; US20070267217A1; SE520714C2; SE0101378L; US7829799B2; SE0101378D0; WO2002086922A1; US7266882B2

Abstract

Manufacturing of miniaturised three-dimentional electric components are presented, as well as components manufactured by the methods. The manufacturing methods comprise micro replication of at least one master structure, e.g. via a mould structure, in at least one polymer layer onto which layer at least one conductive path is provided.

Description

MICRO-REPLICATED MINIATURISED ELECTRIC COMPONENTS

TECHNICAL FIELD

The present invention relates to methods for manufacturing miniaturised electric components, in particular manufacture of miniaturised electric components having a substantially non-flat character with regard to spatial three-dimensional extension.

BACKGROUND

The technique of making small electric components suitable for use in products such as computers and telecommunication equipment has evolved during the last half century into a major branch of industry, producing ever-smaller components. To name an example, the transistor has gone from being a centimetre-sized object in the early days of it's development in the 1940 's and 1950 's to a sub-micrometer object today.

However, there are still obstacles to be overcome in the field of miniaturisation of electric components. In particular, components that require certain spatial properties, i.e. shape, are still difficult to miniaturise while still retaining optimal electric properties. Such components include inductors, transformers, capacitors etc.

Of course, there have been numerous attempts to produce these types of miniaturised components. For example, three-dimensional micro-machined inductors have been studied by several groups . The geometry of the structures are typically solenoids. Examples of the state of the art include the work presented by J. 33. Yoon et al . , "Monolithic integration of 3-D electroplated microstructures with unlimited number of levels using planarization with a sacrificial metallic mold" , IEEE MEMS-1999 as well as US-patent 5,793,272, which shows an integrated toroidal inductor. US 5,793,272 describes a toroidal coil produced by a dual -damascene process. A 1.4 nH coil produced by this process achieved a Q value of 40 at 5.8 GHz.

However, all these state of the art integrated inductors for radio frequency application are based on a planar geometry. The limitations of planar integrated coils are several and include that the Q value of the inductor is limited by self-resonance due to the parasitic capacitance of the coil through capacitive coupling to the substrate. Also the ratio of the inductance and series resistance is not optimal. Secondly, the magnetic field of the inductor couples to the surrounding electronics. Hence, interference with other parts of the electronics limits the density of inductive components on the chip.

Moreover, planar inductors with high Q values are large in terms of silicon surface area, an area that cannot be utilised for any other purpose.

SUMMARY OF THE INVENTION

It is hence an object of the present invention to solve a problem of how to obtain miniaturised electric components having a substantially non-flat character with regard to spatial three-dimensional extension.

In it's most general aspect the present invention solves the problem in that it provides a method for manufacturing a miniaturised three-dimensional electric component. The manufacturing method comprises micro replica- tion of at least one master structure. The replication takes place via a mould structure, e.g. an insert, or a template structure, in at least one polymer layer onto which layer at least one conductive path is provided.

An advantage of the invention in relation to prior art methods for manufacturing miniaturised electric components lies in the fact that the component is realised in a polymer material, as opposed to prior art techniques of utilising, e.g. Silicon wafers. Polymer materials can be formed into more or less arbitrary shapes by casting or by injection moulding or embossing.

Particularly advantageous is the use of the method of the present invention when manufacturing electric inductors, and most notably, arrays of inductors, for use in e.g. small hand held radio devices such as mobile communi- cation terminals. In such devices there is a need for analogue filters, resonators and matching circuits in which LC-circuits are necessary. In such circuits there is an inherent need for inductors having high Q-values, as will be discussed in some detail below in connection with a preferred embodiment of the invention.

Another advantage obtained by the use of polymers to create small-scale components relies on the simple fact that a polymer layer can be used to buffer the thermal expansion mismatch between different layers . The components manufactured by the present inventive method become extremely compact and hence are capable of being located in close proximity to other circuitry that may generate more or less heat and hence create conditions for differential expansion of substrates etc. Polymers are usually poor heat conductors and hence the use of polymers to manufacture the components enables a user to design circuitry where heat-emitting components may be located more or less close to heat sensitive components.

In a first preferred embodiment of the invention, the method is realised in a number of processing steps defining a more or less direct manufacture of a component from a master structure carrying all the required three- dimensional geometry of the component. The method according to the first embodiment comprises the proces- sing steps of copying the master structure to create a mould structure, e.g. an insert. The mould structure is then used in turn to replicate the master structure in a first and second polymer layer. Polymer support structures are hence obtained.

A first conductive path and a second conductive path are then provided onto the respective first and second polymer layers. The two polymer layers are then joined, thereby obtaining the electric component. Alternatively, the conductive path may be provided after joining the polymer layers . As will be discussed further below, the polymer layers and the conductive paths may be obtained by a number of different methods.

In a second preferred embodiment of the invention, the method is realised in a number of processing steps defining manufacture of a component from a master structure carrying the required three-dimensional geometry of the component in a slightly different manner where the master structure is replicated into a template structure for the component to be . The method according to the second embodiment comprises the processing steps of providing a first conductive path and a second conductive path onto a respective first and second template structure. A first polymer layer and a second polymer layer are provided onto the respective first and second template structures, thereby replicating the respective master structures in the respective polymer layers. This results in a first and second polymer layer, i.e. a structure, joined to the respective first and second conductive path. The first and second template structures are then separated from the respective first and second polymer layers and the two polymer layers are then joined, thereby obtaining the electric component.

It is to be noted that the first and the second template structure may be one and the same template structure which is used as the first template structure in an initial polymer layer creation sequence, and in a second sequence as the second template structure.

In a third preferred embodiment of the invention, the method is realised in a number of processing steps defining manufacture of a component from a master structure. In this embodiment a first polymer layer, i.e. a structure, having a conductive path may be obtained either via a more or less direct manufacturing method as discussed in connection with the first embodiment, or as in the second embodiment where a template acts as a support firstly for the conductive path and subsequently the polymer layer. The method according to the third embodiment then further comprises the processing steps of providing a sacrificial structure onto the conductive path on the polymer layer structure already obtained. A second conductive path is then provided onto the sacrificial structure/ whereupon the sacrificial structure can be removed, thereby obtaining the electric component. However, it is not necessary to remove the sacrificial structure.

As in the first preferred embodiment of the invention, in these second and third embodiments the polymer layers and the conductive paths may be obtained by a number of different methods, as will be discussed further below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically a top view of a toroidal inductor manufactured according to the present invention.

Figure 2a-2d shows schematically cross sectional views of substrates during different stages of a first embodiment of a manufacturing method according to the present invention.

Figure 3 shows schematically a cross sectional view of a substrate comprising a ferromagnetic core. Figure 4a-4c shows schematically cross sectional views of substrates during different stages of a second embodiment of a manufacturing method according to the present invention. Figure 5a-5c shows schematically cross sectional views of substrates during different stages of a third embodiment of a manufacturing method according to the present invention.

Figure 6a-d shows schematically cross sectional views of circuits comprising an inductor according to the present invention.

Figure 7 shows schematically a cross sectional view of a circuit comprising an inductor according to the present invention. Figure 8 shows schematically a cross sectional view of a circuit comprising an inductor according to the present invention.

Figure 9 shows a diagram of Q-values for inductors .

PREFERRED EMBODIMENTS The invention in its general form, as discussed above, is related to manufacture of any electric component . In the description to follow below, a number of embodiments of a manufacturing method will be presented. Common to the embodiments is the choice of a toroidal inductor, i.e. a toroidal coil, as representing the electric component to be manufactured. Small-scale inductors are required in many kinds of products, not least in the field of small hand-held devices such as mobile telephone terminals containing high frequency radio transmitters and receivers as well as transformers and baluns . Figure 1 shows. a top view of a toroidal inductor, as it would appear if exposed. As will be shown, however, the toroidal coils manufactured according to the inventive method will after the last step of manufacture be enclosed by a polymer material and not be visible to inspection such as figure 1 suggests. The coil of figure 1 comprises a torus shaped conductive path 101 having connecting ends 102,103. A typical size of such a component is on the order of 10² μm.

The embodiments of the manufacturing method will be presented by use of schematic figures of such an enlarged scale that only one component, i.e. toroidal coil, is visible in each figure. However, it shall be stressed that, when utilising the manufacturing method according to the invention, machinery suitable for manufacturing, e.g., optical discs such as CD or DVD is a preferred choice. As the skilled person will appreciate, the use of such machinery entails producing polymer layers suitable for manufacturing a plurality of components simultaneously .

Three preferred embodiments of the invention will be disclosed with reference to cross sectional views in figures 2-6. The cross sectional views may, e.g., be the AA-section indicated in figure 1. Each embodiment requires a pre-fabricated original or master, which contains the required three-dimensional geometrical features of the final structure of the components. It is assumed that fabrication of the original or master is known to the skilled person and that the skilled person will select the most appropriate method amongst available methods for silicon micromachining.

Referring now to figures 2a-2c, a first embodiment of an inventive manufacturing method will be described. Initially a mould structure or insert 203 is created from the master structure. The mould insert 203 is obtained by electroforming the master, which entails depositing a metal seed-layer onto the master structure, electroplating a thick layer of metal, separating the mould insert 203 from the master and planarising the backside of the mould insert. The mould insert 203 is then replicated by one of three methods. Replication by casting is initiated by forming a cavity between the mould insert 203 and a substrate 202 which is filled with a suitable polymer material 201, thus replicating the mould insert 203.

Alternatively, the mould insert 203 may be replicated by injection moulding or embossing in a suitable polymer. The substrate 202 is then joined at a later stage of the manufacturing process. The mould insert 203 holds the three-dimensional geometry of the final component, i.e. a toroidal coil in the example discussed here, and comprises a semi-torus 204 and a via core structure 205. The substrate 202 on which the polymer layer is provided is preferably part of an electric circuit (not shown) with which the toroidal coil is to be connected by means of a via obtained by the via core structure 205 and a contact pad 230.

After replication of the mould insert 203 by the chosen method, the polymer layer 201 is metallised with a thin conductive layer 206. The thin conductive layer 206 is used as an electrode in a process for application of photoresist by electrodeposition. Electrodeposition provides a conformal coating of photoresist 207 over the three-dimensional geometry of the polymer layer 201. The photoresist 207 is then patterned by methods known to those skilled in the art.

The patterning will entail providing a side-wall pattern for the conductive parts of the component and, as illustrated in figure 1, provide the coil with the conductive path 101 as well as the connecting ends

102,103.

Preferably, the conductive path is provided by electroplating or electroless plating a suitable metal onto the patterned polymer layer 201 prior to joining of the first and second layers. However, the conductive path may be provided by internal plating after joining of the polymer layers. A suitable metal will be selected by the skilled person when using the inventive method.

After provision of the conductive path, the photoresist is removed and the seed layer etched away by methods known in the art to provide separate conductive paths 208.

Referring now to figure 2d, in which is shown a first and a second structure halve 241,242 comprising substrates 202,222 polymer layers 201,221 and conductive layer 208,228 having been subject to the processing steps discussed above in connection with figures 2a-2c. The second structure 242 is aligned with respect to the first structure 241 using visual and mechanical systems that are outside the scope of the present invention. Figure 2d also illustrates a finalised component 240 comprising the two joined structure halves 241,242 created by the method as disclosed above.

Normally, plating of the conductive layer 206,208 is performed prior to the joining of the two halves 241,241 and a conducting joint may be achieved by thermocompression bonding or by a short period of electroless or electrolytic internal plating.

Figure 3 illustrates schematically a step of toroidal coil manufacturing prior to joining of two halves 341,342 similar to the halves 241,242 in figure 2d. On top of substrates 302,322 are respective polymer support structures 301,321 and provided with a ferromagnetic core 304. In low frequency applications, attempts have been made to solve the problem of creating integrated inductors by micro-machining of components. The requirement of low frequency applications is that the inductance value of the coil should be in the range of micro Henrys. In order to create such high inductance values the core of the ω ω DO to ¹

LΠ o in o σi o LΠ

conductive path of a toroidal coil 404 and a via core structure 405 supported by the polymer support structure 403. Further manufacture of a complete toroidal coil is then performed according to the steps described in the first embodiment. Needless to say, one and the same template may be used to manufacture a plurality of polymer structures .

A third embodiment of the inventive method will now be described with reference to figures 5a-5c. A polymer support structure 501 comprising a conductive path 507 is obtained by way of any of the manufacturing methods according to the first or second embodiment discussed above .

A layer of photoresist 503 is deposited onto the polymer support structure 501 and the conductive layer 507 by way of any known technique such as spin coating, spray coating, electrodeposition or possibly casting. All areas except a torus shaped area 504 on top of the conductive layer 507 of the coil is removed by way of exposure and development according to known art, as illustrated in figure 5b. The remaining photo resist is heated leading to a flowing and reshaping of the resist into a more or less rounded torus of photo resist 505, as illustrated in figure 5c. A seed-layer is then provided onto the sacrificial layer and patterned as described above in connection with the first and second embodiments. Electroplating or electroless plating then provides the conductive path to complete the component . The embodiments of manufacturing methods described above may be used to manufacture a number of different miniaturised electric components and circuitry comprising a plurality of such components.

Stand-alone components and systems as exemplified in figure 1 include inductors, arrays of inductors, transformers and arrays of transformers, differing in the way in which the conductive paths, and connections to the paths, are arranged. In figs 6a-6d is shown an electric stand-alone component 600 placed on a multichip module carrier substrate 601 and encapsulated in a polymer support structure 602 In figure 6a, the stand-alone component is, together with other RF circuitry 604, further embedded in a protective polymer encapsulation 603. In figure 6b, the stand-alone component 600 is underfilled with a protective polymer layer 605 instead of being encapsulated.

In figure 6c, the component is a stand-alone component placed, together with other RF circuitry 604, on a printed wiring board 606 and encapsulated in a polymer support structure 602.

In figure 6d, the inventive component 607 is part of a 3- dimensional stacked multichip module 608 on a printed circuit board 604, including other stacked RF circuitry 609 and 610, including various RF, MEMS, processor and memory devices.

In figure 7, the components 612 according to the invention are embedded in a multichip 614 module carrier substrate 611. The multichip modules 614 may be encapsulated 613 and the carrier substrate 611 provided with flip-chip solder bumps 615. Of course any appropriate bonding technique can be used.

In figure 8, the components 616 according to the invention are is embedded in a protective polymer encapsulation 617 above a multichip module 619 carrier substrate 618.

Naturally, the components may also be manufactured such that a carrier polymer substrate contains, apart from the embedded inductor coils, also the vias and interconnecting wires. ω ω to to H

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Claims

1. A method for manufacturing a miniaturised three-dimensional electric component comprising micro replication of at least one master structure in at least one polymer layer onto which layer at least one conductive path is provided.

2. A method according to claim 1, comprising: copying the at least one master structure into at least one mould structure, replicating the at least one mould structure in a respective first and second polymer layer thereby obtaining a first and a second polymer support structure, providing a first conductive path and a second conductive path onto the respective first and second polymer support structure, joining the two polymer support structures, thereby obtaining the electric component .

3. A method according to claim 2, wherein the replication of the at least one mould structure precedes the provision of the conductive path onto the polymer support structures which in turn precedes the joining of the polymer support structures .

4. A method according to claim 2, wherein the replication of the at least one mould structure precedes the joining of the polymer support structures which in turn precedes the provision of the conductive path onto the polymer support structures .

5. A method according to any one of claims 1-4, wherein the replication of the mould structure comprises embossing.

6. A method according to any one of claims 1-4, wherein the replication of the mould structure comprises casting.

7. A method according to any one of claims 1-4, wherein the replication of the mould structure comprises injection moulding.

8. A method according to any one of claims 1-7, wherein the provision of conductive paths at least partly comprises electroplating.

9. A method according to any one of claims 1-7, wherein the provision of conductive paths at least partly comprises electroless plating.

10. A method according to any one of claims 8-9, wherein electroplating of the two polymer support structures precedes the joining of the support structures and whereupon electric connection between the conductive paths on the support structures is secured by way of electroless plating.

11. A method according to any one of claims 8-10, comprising providing a plating seed-layer prior to plating of the conductive paths.

12. A method according to any one of claims 1-11, wherein the seed-layer is patterned by use of an electrodeposited photoresist to provide a side-wall pattern prior to plating the conductive paths. 13. A method according to any one of claims 1-12, wherein the joining comprises thermocompression.

14. A method according to claim 1, comprising: replicating the at least one master structure into at least one template structure, providing a first conductive path and a second conductive path onto a respective first and second template structure, providing a first polymer layer and a second polymer layer onto the respective first and second template structures, thereby replicating the respective master structures in the respective polymer layers resulting in a first and second polymer support structure joined to the respective first and second conductive path, separating the first and second template structure from the respective first and second polymer support structure, joining the two polymer support structures, thereby obtaining the electric component .

15. A method according to claim 14, wherein the provision of the polymer layers comprises embossing.

16. A method according to claim 14, wherein the provision of the polymer layers comprises casting.

17. A method according to claim 14, wherein the provision of the polymer layers comprises injection moulding. 18. A method according to any one of claims 14-17, wherein the provision of conductive paths at least partly comprises electroplating.

19. A method according to any one of claims 14-17, wherein the provision of conductive paths at least partly comprises electroless plating.

20. A method according to any one of claims 18-19, wherein electric connection between the conductive paths on the support structures is secured by way of electroless plating subsequent to the joining of the support structures.

21. A method according to any one of claims 18-20, comprising providing a plating seed layer prior to plating of the conductive paths.

22. A method according to any one of claims 14-21, wherein the seed-layer is patterned by use of an electrodeposited photoresist to provide a side-wall pattern prior to plating the conductive paths.

23. A method according to any one of claims 14-22, wherein the joining comprises thermocompression. 24. A method according to claim 1, comprising: copying the at least one master structure into a mould structure, replicating the mould structure in a first polymer layer thereby obtaining a first polymer support structure, providing a first conductive path onto the first polymer support structure, providing a sacrificial structure onto the conductive path on the first polymer support structure, providing a second conductive path onto the sacrificial structure, thereby obtaining the electric component .

25. A method according to claim 24, comprising: removing the sacrificial structure.

26. A method according to any one of claims 24-25, wherein the provision of the polymer layers comprises embossing.

27. A method according to any one of claims 24-25, wherein the provision of the polymer layers comprises casting.

28. A method according to any one of claims 24-25, wherein the provision of the polymer layers comprises injection moulding. 29. A method according to any one of claims 24-28, wherein the provision of conductive paths at least partly comprises electroplating.

30. A method according to any one of claims 24-28, wherein the provision of conductive paths at least partly comprises electroless plating.

31. A method according to any one of claims 29-30, comprising providing a plating seed layer prior to plating of the conductive paths.

32. A method according to any one of claims 24-31, wherein the seed-layer is patterned by use of an electrodeposited photoresist to provide a side-wall pattern prior to plating the conductive paths.

33. A method according to claim 1, comprising: replicating the at least one master structure into a template structure, providing a first conductive path onto the template structure, providing a first polymer layer onto the template structure, thereby replicating the master structure in the polymer layer resulting in a first polymer support structure joined to the first conductive path, separating the template structure from the first polymer support structure, providing a sacrificial structure onto the conductive path on the first polymer support structure, providing a second conductive path onto the sacrificial structure, thereby obtaining the electric component . 3 . A method according to claim 33, comprising: removing the sacrificial structure.

35. A method according to any one of claims 33-34, wherein the provision of the polymer layers comprises embossing. 36. A method according to any one of claims 33-34, wherein the provision of the polymer layers comprises casting.

37. A method according to any one of claims 33-34, wherein the provision of the polymer layers comprises injection moulding.

38. A method according to any one of claims 33-37, wherein the provision of conductive paths at least partly comprises electroplating.

39. A method according to any one of claims 33-37, wherein the provision of conductive paths at least partly comprises electroless plating.

40. A method according to any one of claims 38-39, comprising providing a plating seed layer prior to plating of the conductive paths.

41. A method according to any one of claims 33-40, wherein the seed-layer is patterned by use of an electrodeposited photoresist to provide a side-wall pattern prior to plating the conductive paths. 42. A method for manufacturing a miniaturised toroidal inductor coil according to any one of claims 1-41.

43. A method according to claim 42, comprising providing the toroidal coil with a ferromagnetic core.

44. A method according to claim 43, wherein the provision of a ferromagnetic core is performed at least partly by providing a solid ferromagnetic core.

45. A method according to claim 43, wherein the provision of a ferromagnetic core is performed at least partly by way of injection of ferromagnetic material. 46. System comprising at least one miniaturised three- dimensional electric component, said component comprising at least one polymer support structure, micro replicated from at least one master structure, on which polymer structure at least one conductive path is provided. 47. System according to claim 46, wherein the component is a stand-alone component placed on a multichip module carrier substrate and encapsulated in a polymer support structure .

48. System according to claim 47, wherein the stand-alone component is embedded in a protective polymer encapsulation.

49. System according to claim 47, wherein the stand-alone component is underfilled with a protective polymer layer.

50. System according to claim 47, wherein the component is a stand-alone component placed on a printed wiring board and encapsulated in a polymer support structure.

51. System according to any of the claims 47-50, wherein the at least one conductive path at least partly surrounds the at least one polymer support structure .

52. System according to claim 46, wherein the component is constituting part of a 3 -dimensional stacked multichip module .

53. System according to claim 46, wherein the component is embedded in a multichip module carrier substrate.

54. System according to claim 46, wherein the component is embedded in a protective polymer encapsulation above a multichip module carrier substrate.

55. System according to any of the claims 52-54, wherein the at least one polymer support structure at least partly surrounds the at least one conductive path.

56. System according to any one of claims 46-55, wherein at least one component is any one of:

- inductor, - transformer,

- inductor with ferromagnetic core,

- sensor for a flux gate magnetometer,

- capacitor,

- resistor, - sensor electrode for electrochemical measurements.

57. Electric component comprising at least one polymer support structure, micro replicated from at least one master structure, on which polymer structure at least one conductive path is provided. 58. Electric component according to claim 57, wherein the component is a stand-alone component placed on a multichip module carrier substrate and encapsulated in a polymer support structure .

59. Electric component according to claim 58, wherein the stand-alone component is embedded in a protective polymer encapsulation .

60. Electric component according to claim 58, wherein the stand-alone component is underfilled with a protective polymer layer.

61. Electric component according to claim 57, wherein the component is a stand-alone component placed on a printed wiring board and encapsulated in a polymer support structure . 62. Electric component according to any of the claims 58- 61, wherein the at least one conductive path at least partly surrounds the at least one polymer support structure .

63. Electric component according to claim 57, wherein the component is constituting part of a 3 -dimensional stacked multichip module .

64. Electric component according to claim 57, wherein the component is embedded in a multichip module carrier substrate . 65. Electric component according to claim 57, wherein the component is embedded in a protective polymer encapsulation above a multichip module carrier substrate.

66 . Electric component according to any of the claims 63-

65, wherein the at least one polymer support structure at least partly surrounds the at least one conductive path.

67. Electric component according to any one of claims 57-

66, where the component is any one of:

- inductor,

- transformer, - inductor with ferromagnetic core,

- sensor for a flux gate magnetometer,

- capacitor,

- resistor,

- sensor electrode for electrochemical measurements.